This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. There have been no unanticipated problems nor adverse events to report. It is clear that the ID50 for Norwalk virus is extremely low and that 4.8 RT-PCR units is the right dose for future vaccine candidate development work. We are still blind to the regimen of the last group studied (n=5), but only one developed a mild cases of shrot-term gastroenteritis that resolved within a day. Another had a sub-clinical infection. We can only assume that 0.48 RT-PCR units is too low to cause infection.